Use of carboxylic esters as fuel additives or lubricant additives and their preparation

ABSTRACT

Carboxylic esters of the formula I 
     
         R.sup.1 --CO--O--R.sup.2                                   I, 
    
     where 
     R 1  is an aliphatic, straight-chain or branched hydrocarbon radical having alkyl side chains and a number average molecular weight of from 250 to 5000 and 
     R 2  is a straight-chain or branched hydrocarbon radical of 1 to 30 carbon atoms or a radical of the formula II ##STR1## where R 3 , R 4 , R 5  and R 6 , independently of one another, are each hyrogen, branched or straight-chain alkyl, an aromatic radical or an araliphatic radical which may also contain heteroatoms, 
     R 7  and R 8 , independently of one another, are each branched or straight-chain alkyl or an aromatic or araliphatic radical which may also contain heteroatoms, 
     X is O, S, NR 9  or PR 9 , where R 9  is an aliphatic or aromatic radical, 
     n and m, independently of one another, are each from 2 to 20, and 
     x is from 0 to 30, 
     are used as fuel additives or lubricant additives, and fuel compositions or lubricant compositions contain these additives. Carboxylic acids or carboxylic esters are prepared by reacting polymers having at least 30 carbon atoms and at least one carbon--carbon double bond with carbon monoxide and water or an alcohol.

This application is a 371 of PCT/EP95/00429 filed Feb. 7, 1995. Thepresent invention relates to the use of carboxylic esters of the formulaI

    R.sup.1 --CO--O--R.sup.2                                   I,

where

R¹ is an aliphatic, straight-chain or branched hydrocarbon radicalhaving alkyl side chains and a number average molecular weight of from250 to 5000 and

R² is a straight-chain or branched hydrocarbon radical of 1 to 30 carbonatoms or a radical of the formula II ##STR2## where R³, R⁴, R⁵ and R⁶,independently of one another, are each hydrogen, branched orstraight-chain alkyl, an aromatic radical or an araliphatic radicalwhich may also contain heteroatoms,

R⁷ and R⁸, independently of one another, are each branched orstraight-chain alkyl or an aromatic or araliphatic radical which mayalso contain heteroatoms,

X is O, S, NR⁹ or PR⁹, where R⁹ is an aliphatic or aromatic radical,among which O is preferred,

n and m, independently of one another, are each from 2 to 20, preferably2, and

x is from 0 to 30, preferably 0,

as fuel additives or lubricant additives, and fuel compositions orlubricant compositions containing these additives.

The present invention furthermore relates to an improved process for thepreparation of carboxylic acids or carboxylic esters by reactingpolymers of at least 30 carbon atoms, which carry at least onecarbon--carbon double bond, with carbon monoxide and water or alcohols.

Carburettors and intake systems of gasoline engines, but also injectionsystems for fuel metering in gasoline and diesel engines, areincreasingly being contaminated by impurities caused by dust particlesfrom the air, uncombusted hydrocarbon residues from the combustion spaceand the crank case vent gases passed into the carburettor.

These residues shift the air/fuel ratio during idling and in the lowerpart-load range so that the mixture becomes richer and the combustionless complete and in turn the amounts of uncombusted or partiallycombusted hydrocarbons in the exhaust gas become larger and the gasolineconsumption increases.

It is known that these disadvantages can be avoided by using fueladditives for keeping valves and carburettors or injection systems,clean (cf. for example: M. Rossenbeck in Katalysatoren, Tenside,Mineraloladditive, editors J. Falbe, and U. Hasserodt, page 223, G.Thieme Verlag, Stuttgart 1978).

Today, a distinction is made between two generations on the basis of themode of action as well as the preferred site of action of such detergentadditives.

The first generation of additives was capable only of preventing theformation of deposits in the intake system but not of removing existingdeposits, whereas the modern additives of the second generation can doboth (keep-clean and clean-up effect) and can do so in particularbecause of their excellent heat stability in zones of relatively hightemperature, ie. in the intake valves.

The molecular structural principle of these additives which act asdetergents can be stated generally as the linking of polar structures togenerally relatively high molecular weight, nonpolar or oleophilicradicals.

Compounds which are of particular interest here are those which areobtained by means of chlorine-free synthesis methods, since the use ofchlorine results in the occurrence of chlorine- or chloride-containingproducts, which is by no means desirable today.

Such detergents, which may originate from a large number of classes ofchemical substances, are generally used in combination with a carrieroil. The carrier oils have an additional wash function, often supportand promote the detergents in their action and may help to reduce therequired amount of detergent. The carrier oils usually used are viscous,high-boiling and in particular heat-stable liquids. They coat the hotmetal surface (for example the intake valves) with a thin liquid filmand thus prevent or delay the formation or deposition of decompositionproducts on the metal surfaces. Suitable carrier oils are, for example,high-boiling, refined mineral oil fractions, as well as syntheticliquids, such as oil-soluble adducts of alkylene oxides with alcohols.

Owing to the frequently only small detergent effect of the compoundsused as carrier liquids, and a correspondingly small contribution to theoverall performance of an additive package with regard to detergency,the saving of necessary detergents is not optimum and the carrier oilsthemselves must be used in relatively high doses. Usually, such carrieroils can by no means render the use of detergents unnecessary.

It is an object of the present invention to provide a fuel additive orlubricant additive which can be used as a carrier oil and has apronounced detergent effect.

EP-A-148 592 relates to the preparation of carboxylic esters frompolymers which carry a carbon--carbon double bond, with carbon monoxideand an alcohol in the presence of a protic acid and of a catalyst whichcontains at least one of the metals palladium, rhodium, ruthenium,iridium and cobalt, and copper. The products are detected by IRspectroscopy. The conversion or selectivity of this reaction is notevident from the data in the publication. When the experiments describedwere repeated, it was found that the conversion of the desired productsis less than 10%. However, such a yield is economically unacceptable.

DE-A 29 12 489 describes the preparation of carboxylic esters byhydroformylation of internal olefins which carry not more than 20 carbonatoms in the presence of a cobalt catalyst under from 150 to 300 bar.

It is a further object of the invention to provide a process for thepreparation of carboxylic acids and carboxylic esters from polymerswhich still carry a carbon--carbon double bond. Such a process shouldmake it possible to obtain the desired products with good conversion andhigh selectivity.

We have found that these objects are achieved by the use, defined at theoutset, of carboxylic esters of the formula I.

The present invention furthermore relates to fuel compositions whichcontain carboxylic esters of the formula I in an amount of from 10 to5000 ppm, in particular from 100 to 2000 ppm.

The present invention also relates to lubricant compositions whichcontain carboxylic esters of the formula I in an amount of from 0.5 to15, in particular from 0.5 to 10, % by weight.

The present invention also relates to a process for the preparation ofcarboxylic acids or carboxylic esters, according to which polymers whichhave at least 30 carbon atoms and carry at least one carbon-carbondouble bond are reacted with carbon monoxide and water or alcohols inthe presence of catalytic amounts of a metal or of a metal compound ofgroups 8 to 10 of the Periodic Table. In the process, the reactionpressure is from 50 to 600 bar.

According to the invention, carboxylic esters of the formula I in whichR¹ has a number average molecular weight of from 500 to 2500,particularly preferably from 700 to 1500, are preferably used.

In general, R¹ is a hydrocarbon radical which is obtainable bypolymerization of olefins, the polymerization being carried out in sucha way that the chain termination leads to a double bond (for example, bycationic or coordinate polymerization). These olefins are in general C₂-C₃₀ -olefins, preferably C₂ -C₆ -olefins, particularly preferably C₂-C₄ -olefins, among these in turn isobutene being particularlypreferred. Both homopolymers and copoly- mers, for example polymers offrom 70 to 95 mol% of isobutene and from 5 to 30 mol% of 1-butene, aresuitable. As a result of their preparation process, these polyolefinsgenerally consist of a mixture of compounds of different molecularweights. The carboxylic esters used according to the invention may beobtained, for example, by the process stated in EP-A 0 148 592.

However, novel carboxylic esters are preferably prepared by thefollowing process from polymers having at least 30 carbon atoms:

The polymers to be used as starting material carry at least 30 carbonatoms and at least one carbon-carbon double bond. Polymers having onecarbon-carbon double bond are preferred. Preferred among these arehydrocarbon polymers which are composed of aliphatic monoolefins, suchas ethylene, propylene, n-butene, isobutene, hexene or mixtures of thesemonomers. The molecular weights are as a rule from 450 to 7000.Polypropenes and polyisobutenes which in general have molecular weightsof from 450 to 3000, preferably from 700 to 1200, are particularlypreferred. Such compounds are obtainable, for example, according to EP-A481 297. Propene oligomers may be obtained, for example, according toChem. Lett. (1991), 1525.

Catalysts used in the novel process are metals or metal compounds ofgroups 8 to 10 of the Periodic Table. These may be used as heterogeneousor, preferably, homogeneous catalysts. Examples of suitable metalcompounds are the chlorides, acetates and nitrates of the stated metals,but the metals may also be used in elemental form. Cobalt, palladium andrhodium are preferred, as well as compounds thereof. Cobalt carbonylcompounds and cobalt salts are particularly preferred.

Carbon monoxide is used in excess in the reaction. The ratio of carbonmonoxide to the polymer is established by means of the partial pressureof the carbon monoxide.

The polymer is reacted with carbon monoxide and with water or analcohol. These alcohols are as a rule primary or secondary aliphatic C₁-C₂₀ -alcohols, such as methanol, ethanol, isopropanol, n-propanol,n-butanol and 2-ethylhexanol, and C_(2-C) ₃₀ -amino-alcohols, such as2-dimethylaminoethanol, 2-diethylaminoethanol,2-diisopropylaminoethanol, 3-dimethylamino-1-propanol,3-diethylamino-1-propanol, 3-diisopropylamino-1-propanol,1-dimethylamino-2-propanol, 1-diethylamino-2-propanol,1-diisopropyl-amino-2-propanol and 3-dimethylamino-1,2-propanediol,araliphatic C₇ -C₁₂ -alcohols, such as benzyl alcohol, aromatic C₆ -C₁₀-alcohols, such as phenol, and C₂ -C₂₀ -mono- and polyalkylene glycolsand monoethers, such as ethylene glycol, ethylene glycol monomethylether and diethylene glycol, diethylene glycol monomethyl ether,triethylene glycol, triethylene glycol monomethyl ether, tetraethyleneglycol and tetraethylene glycol monomethyl ether. In general, from 1 to30, preferably 10 to 25, mol of water or alcohol are use per mol ofpolymer compound. A reaction with water leads to the corresponding acid,while a reaction with alcohols leads to the esters.

The novel process is preferably carried out in the presence ofnitrogen-containing bases. Tertiary aromatic amines, such as pyridine orpicolines, have proven particularly suitable. These bases may be used ina molar ratio of from 1:1 to 50:1, preferably from 2:1 to 15:1, based onthe catalytically active metal.

As a rule, the molar ratio of the polymer to the catalytically activemetal is from 2:1 to 50:1, preferably from 4:1 to 15:1.

The reaction can be carried out in a solvent. The solvents are ingeneral polar solvents, such as acetone, and ethers, such astetrahydrofuran, but also the alcohols or water occurring as reactantsin the reaction. These solvents may also be used as a mixture withhydrocarbons, such as alkanes. The amount of the solvent is in generalfrom 10 to 90% by weight, based on the total batch.

The reaction can be carried out at from 20° to 300° C., preferably from100° to 200° C. The reaction pressure is from 50 to 600, preferably from100 to 300, bar absolute pressure. The reaction times are in generalfrom 5 to 48 hours. For carrying out the reactions, the reactants aremixed and then brought to the reaction temperature under CO pressure.Working up can be carried out in a manner known per se, by separatingoff the catalyst, distilling off the solvent and purifying the reactionproduct by chromatography.

The reaction can be carried out continuously or batchwise.

The novel process permits the preparation of the products with highselectivity of the addition reaction of the carbon monoxide and thewater or the alcohol and with good conversion.

The novel use of esters of the formula I as fuel additives, inparticular for gasoline engines, permits combination with knowndetergents, for example polyisobutylamines, as obtainable, for example,by hydroformylation of polyisobutene, followed by reductive amination,and dispersants as the carrier oil components or as the sole detergentcomponents.

Used as lubricant additives, the compounds of the formula I may also beused in combination with further conventional additives, for examplecorrosion inhibitors, antiwear additives, detergents, antioxidants andpour point improvers.

The detergent component used in the mixture with the novel substancescan in principle be any known product suitable for this purpose, asdescribed, for example, in J. Falbe and U. Hasserodt, Katalysatoren,Tenside und Mineraloladditive, G. Thieme Verlag, Stuttgart 1978, page221 et seq. or in K. Owen, Gasoline and Diesel Fuel Additives, JohnWiley & Sons, 1989, page 23 et seq.

N-containing detergents, for example compounds which contain an amino oramido group, are preferably used. Polyisobutylamines according to EP-A-0244 616, ethylenediaminetetraacetamides and/or -imides according toEP-A-0 188 786 or polyetheramines according to EP-A-0 244 725 areparticularly suitable, reference being made to the definitions in thesepublications. As a result of their preparation, the products describedthere likewise have the advantage of being chlorine- or chloride-free.

The novel carboxylic esters may also be combined with conventionalcarrier oils. Particularly suitable carrier oils are those based onpolyglycol, for example corresponding ethers and/or esters, as describedin U.S. Pat. No. 5,004,478 or DE-A-38 38 918. Polyoxyalkylenemonoolshaving terminal hydrocarbon groups (U.S. Pat. No. 4,877,416) or carrieroils as disclosed in DE-A-41 42 241 may also be used.

Suitable fuels for gasoline engines are leaded and in particularunleaded regular and premium gasoline. The gasolines may also containcomponents other than hydrocarbons, for example alcohols, such asmethanol, ethanol or tert-butanol, and ethers, eg. methyl tert-butylether. In addition to the novel additives, the fuels also contain, as arule, further additives, such as corrosion inhibitors, stabilizers,antioxidants and/or further detergents.

Corrosion inhibitors are generally ammonium salts of organic carboxylicacids which tend to form films because the starting compounds have anappropriate structure. Furthermore, amines for lowering the pH arefrequently present in corrosion inhibitors. Heterocyclic aromatics aregenerally used for preventing corrosion of nonferrous metals.

Even in a small dose, the novel carboxylic esters make a largecontribution to the overall performance of an additive package withregard to detergency. This makes it possible in general to savedetergents, and the use of further additional detergents may even besuperfluous in specific cases.

EXAMPLE 1

Preparation of methyl polyisobutanecarboxylate

900 g of polyisobutene (molecular weight 1100; 0.82 mol), 19.2 g ofdicobalt octacarbonyl (56 mmol), 168 g of 3-picoline (1.8 mol) , 600 gof methanol (18.8 mol) and 900 g of a C₁₀ -C₁₃ -alkane mixture wereinitially taken in an autoclave. CO was forced in to a pressure of 50bar. The autoclave was heated to 180° C. and the CO pressure wasincreased to 270 bar. After 24 hours, air was passed in in order toremove the catalyst, the solvent and the picoline were separated off bydistillation, and 920 g of a viscous product containing 71% of methylpolyisobutanecarboxylate remained. The conversion was 80% and theselectivity 89%. With pentane as solvent, the ester could be separatedfrom the unconverted starting material by chromatography over silicagel.

Engine tests

EXAMPLE 2

In Examples 2a and 2b , dimethylaminoethyl polyisobutanecarboxylate,which was prepared starting from polyisobutene having a number averagemolecular weight of 1000 by a method similar to that of Example 1 usingdimethylaminoethanol instead of methanol or by transesterification ofmethyl polyisobutanecarboxylate with dimethylaminoethanol, was tested asa fuel additive in engine tests.

The engine tests were carried out in an Opel Kadett 1.2 l engineaccording to CEC F/04/A/87. Fuel used: unleaded European premium grade.

The dose of dimethylaminoethyl polyisobutanecarboxylate and the resultsobtained are shown in the table.

                  TABLE    ______________________________________                    Intake valve deposits  mg!*)           Dose     Valves    Example   ppm!      1      2       3    4    ______________________________________    2a       400        15     0        3   0                        (278)  (132)   (191)                                            (180)    2b       200        22     7       10   1                        (278)  (132)   (191)                                            (180)    ______________________________________     *)Values in brackets: deposits without introduction of additive; the     different values are due to differences in the unleaded European premium     grade used.

EXAMPLE 3

In Examples 3a and 3b, methyl polyisobutanecarboxylate which wasprepared according to Example 1 was tested as a fuel additive in enginetests.

The engine tests were carried out in an Opel-Kadett 1.2 l engineaccording to CEC F/04/A/87. Fuel used: unleaded European premium grade.

The dose of methyl polyisobutanecarboxylate and the results obtained areshown in the table.

                  TABLE    ______________________________________                    Intake valve deposits  mg!*)           Dose     Valves    Example   ppm!      1      2       3    4    ______________________________________    3a       400         4     0       6    6                        (210)  (150)   (154)                                            (200)    3b       200        16     0       2    8                        (278)  (132)   (191)                                            (180)    ______________________________________     *)Values in brackets: deposits without introduction of additive; the     different values are due to differences in the unleaded European premium     grade used.

We claim:
 1. A process for introducing additives into fuels, whereincarboxylic esters of the formula I

    R.sup.1 --CO--O--R.sup.2                                   (I)

where R¹ is an aliphatic, straight-chain or branched hydrocarbon radicalhaving alkyl side chains and a number average molecular weight of from250 to 5000 and R² is a straight-chain or branched hydrocarbon radicalof 1 to 30 carbon atoms or a radical of the formula II ##STR3## whereR³,R⁴,R⁵ and R⁶, independently of one another, are each hydrogen,branched or straight-chain alky, an aromatic radical or an araliphaticradical which may also contain heteroatoms, R⁷ and R⁸, independently ofone another, are each branched or straight-chain alkyl or an aromatic oraraliphatic radical which may also contain heteroatoms, X is O, S, NR⁹or PR⁹, where R⁹ is an aliphatic or aromatic radical, n and m,independently of one another, are each from 2 to 20, and x is from 0 to30,which have been prepared by reacting the corresponding polymersforming the basis of R¹ and having at least one carbon--carbon doublebond with carbon monoxide and with alcohols of the formula R² --OH inthe presence of catalytic amounts of a metal or of a metal compound ofgroups 8 to 10 of the Periodic Table and in the presence of anitrogen-containing base at from 50 to 600 bar, are introduces asadditives.
 2. The process defined in claim 1, wherein R¹ has a numberaverage molecular weight of from 500 to
 2500. 3. A fuel compositionwhich contains of from 10 to 5000 ppm of a carboxylic ester of theformula I

    R.sup.1 --CO--O--R.sup.2                                   ( 1)

where R¹ is an aliphatic, straight-chain or branched hydrocarbon radicalhaving alkyl side chains and a number average molecular weight of from250 to 5000 and R² is a straight-chain or branched hydrocarbon radicalof 1 to 30 carbon atoms or a radical of the formula II ##STR4## whereR³,R⁴,R⁵ and R⁶, independently of one another, are each hydrogen,branched or straight-chain alkyl, an aromatic radical or an araliphaticradical which may also contain heteroatoms, R⁷ and R⁸, independently ofone another, are each branched or straight-chain alkyl or an aromatic oraraliphatic radical which may also contain heteroatoms, X is O, S, NR⁹or PR⁹, where R⁹ is an aliphatic or aromatic radical, n and m,independently of one another, are each from 2 to 20, and x is from 0 to30, which have been prepared by reacting the corresponding polymersforming the basis of R¹ and having at least one carbon--carbon doublebond with carbon monoxide and with alcohols of the formula R² --OH inthe presence of catalytic amounts of a metal or of a metal compound ofgroups 8 to 10 of the Periodic Table and in the presence of anitrogen-containing base at from 50 to 600 bar.
 4. The process definedin claim 1 wherein the carboxylic esters have been prepared frompolyisobutene as the corresponding polymer forming the basis of R¹. 5.The process defined in claim 1 wherein the carboxylic esters have beenprepared from polypropene or polyisobutene as the corresponding polymerforming the basis of R¹.
 6. The process defined in claim 5 wherein thepolypropene or polyisobutene has a molecular weight of from 450 to 3000.